package web

import (
	"errors"
	"io"
	"mime"
	"net/http"
	"os/exec"
	"path"
	"slices"
	"strconv"
	"strings"

	"github.com/gabriel-vasile/mimetype"

	"hearthforge/internal/db"
	"hearthforge/internal/gitcmd"
	"hearthforge/internal/highlight"
	"hearthforge/internal/markdown"
	"hearthforge/internal/util"
	"hearthforge/internal/web/views"
)

// rawSandboxCSP is sent with every /raw response the browser would parse as a
// document (HTML, SVG, XML). `sandbox` without allow-same-origin gives the
// document an opaque origin: no cookies, no storage, and no readable fetch
// of anything on this server. No allow-scripts, so nothing runs at all.
// A raw file on our origin could otherwise act as the viewer, which is a
// stored-XSS path. Every other type gets no policy, so previews work.
const rawSandboxCSP = "sandbox; default-src 'none'; img-src 'self' data:; " +
	"style-src 'unsafe-inline'; font-src 'self' data:; frame-ancestors 'none'"

// isDocumentType reports whether a browser parses this MIME type as a
// scripting document. It reads the declared type, the same value that goes
// into Content-Type, so the render and sandbox decisions cannot drift apart.
func isDocumentType(contentType string) bool {
	base := strings.ToLower(strings.TrimSpace(strings.SplitN(contentType, ";", 2)[0]))
	switch base {
	case "text/html", "application/xhtml+xml", "image/svg+xml", "text/xml", "application/xml":
		return true
	}
	return strings.HasSuffix(base, "+xml")
}

// treeRoot lists the repository root at a ref.
func (s *Server) treeRoot(w http.ResponseWriter, r *http.Request) {
	s.renderTree(w, r, "")
}

// treePath lists a subdirectory, or redirects to the blob view for a file.
func (s *Server) treePath(w http.ResponseWriter, r *http.Request) {
	s.renderTree(w, r, refParam(r, "*"))
}

func (s *Server) renderTree(w http.ResponseWriter, r *http.Request, subpath string) {
	repo, ok := s.visibleRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	resolved, err := s.Git.ResolveRef(r.Context(), repo.Name, ref)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	entries, err := s.Git.LsTree(r.Context(), repo.Name, ref, subpath)
	if err != nil {
		http.Error(w, "Not found", gitStatusCode(err))
		return
	}
	if subpath != "" && len(entries) == 0 {
		// An empty listing means the path is a file, not a directory.
		redirectTo(w, r, "/"+repo.Name+"/blob/"+views.EscapePath(ref)+"/"+views.EscapePath(subpath))
		return
	}
	branches, _ := s.Git.Branches(r.Context(), repo.Name)
	tags, _ := s.Git.Tags(r.Context(), repo.Name)

	readme := s.readme(r, repo.Name, ref, subpath, resolved, entries)
	views.Render(w, http.StatusOK, views.FileTree(s.Cfg, User(r), repo, ref, subpath,
		entries, branches, tags, readme))
}

func (s *Server) blobView(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.visibleRepo(w, r)
	if !ok {
		return
	}
	s.renderBlob(w, r, repo, http.StatusOK, r.URL.Query().Get("error"))
}

// renderBlob shows the file at the ref and path of the request URL.
func (s *Server) renderBlob(w http.ResponseWriter, r *http.Request, repo *db.Repo, status int, blobError string) {
	ref := refParam(r, "ref")
	filePath := refParam(r, "*")
	filename := path.Base(filePath)

	// Everything below reads at one commit, which the delete form sends as its base.
	commitSHA, err := s.Git.ResolveRef(r.Context(), repo.Name, ref)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	// Check the size before reading the blob. Holding a huge buffer and then
	// highlighting it is the cheapest denial-of-service against a public repo.
	size, sizeErr := s.Git.FileSize(r.Context(), repo.Name, commitSHA, filePath)
	if sizeErr == nil && size > s.Cfg.MaxRenderBytes {
		branches, _ := s.Git.Branches(r.Context(), repo.Name)
		tags, _ := s.Git.Tags(r.Context(), repo.Name)
		views.Render(w, status, views.FileBlob(s.Cfg, User(r), repo, ref, filePath, commitSHA,
			highlight.FileView{Type: "download", Size: size}, branches, tags, "", blobError))
		return
	}

	content, err := s.Git.Show(r.Context(), repo.Name, commitSHA, filePath)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	branches, _ := s.Git.Branches(r.Context(), repo.Name)
	tags, _ := s.Git.Tags(r.Context(), repo.Name)

	cacheKey := repo.Name + ":" + commitSHA + ":" + filePath
	view := s.HL.ServeFile(content, filename, cacheKey)

	markdownHTML := ""
	if markdownExt.MatchString(filename) {
		dir := path.Dir(filePath)
		if dir == "." {
			dir = ""
		}
		markdownHTML = s.MD.Render(string(content), cacheKey,
			&markdown.Context{Repo: repo.Name, Ref: ref, Dir: dir})
	}
	views.Render(w, status, views.FileBlob(s.Cfg, User(r), repo, ref, filePath, commitSHA,
		view, branches, tags, markdownHTML, blobError))
}

// rawFile streams a blob straight from git. It never buffers the whole file.
func (s *Server) rawFile(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.visibleRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	filePath := refParam(r, "*")
	total, err := s.Git.FileSize(r.Context(), repo.Name, ref, filePath)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	if s.Cfg.MaxRawDownloadBytes > 0 && total > s.Cfg.MaxRawDownloadBytes {
		http.Error(w, "File exceeds raw download size limit", http.StatusRequestEntityTooLarge)
		return
	}
	filename := path.Base(filePath)

	head, err := s.blobHead(r, repo.Name, ref, filePath)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	contentType := sniffContentType(filename, head)

	body, stop, err := s.blobStream(r, repo.Name, ref, filePath)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	defer stop()

	start, length, partial := parseRange(r.Header.Get("Range"), total)
	h := w.Header()
	h.Set("Content-Type", contentType)
	h.Set("Accept-Ranges", "bytes")
	if isDocumentType(contentType) {
		h.Set("Content-Security-Policy", rawSandboxCSP)
	}
	if partial {
		h.Set("Content-Range", "bytes "+strconv.FormatInt(start, 10)+"-"+
			strconv.FormatInt(start+length-1, 10)+"/"+strconv.FormatInt(total, 10))
		h.Set("Content-Length", strconv.FormatInt(length, 10))
		w.WriteHeader(http.StatusPartialContent)
		if start > 0 {
			if _, err := io.CopyN(io.Discard, body, start); err != nil {
				return
			}
		}
		_, _ = io.CopyN(w, body, length)
		return
	}
	h.Set("Content-Disposition", util.ContentDisposition("inline", filename))
	h.Set("Content-Length", strconv.FormatInt(total, 10))
	_, _ = io.Copy(w, body)
}

// blobStream starts `git cat-file blob` and returns its stdout. The returned
// stop function kills git, which matters when a client disconnects early.
// cat-file is used over `git show` so the streamed bytes match the size
// cat-file -s reported, even on repos with smudge filters.
func (s *Server) blobStream(r *http.Request, repoName, ref, filePath string) (io.Reader, func(), error) {
	if !gitcmd.ValidRef(ref) || !gitcmd.ValidPath(filePath) {
		return nil, nil, gitcmd.ErrInvalidRef
	}
	cmd := exec.CommandContext(r.Context(), "git", "-C", s.Git.RepoPath(repoName),
		"cat-file", "blob", ref+":"+filePath)
	cmd.Env = gitcmd.Env()
	out, err := cmd.StdoutPipe()
	if err != nil {
		return nil, nil, err
	}
	if err := cmd.Start(); err != nil {
		return nil, nil, err
	}
	stop := func() {
		_ = out.Close()
		_ = cmd.Process.Kill()
		_ = cmd.Wait()
	}
	return out, stop, nil
}

// blobHead reads the first bytes of a blob for content sniffing.
func (s *Server) blobHead(r *http.Request, repoName, ref, filePath string) ([]byte, error) {
	body, stop, err := s.blobStream(r, repoName, ref, filePath)
	if err != nil {
		return nil, err
	}
	defer stop()
	head := make([]byte, highlight.BinaryDetectBytes)
	n, err := io.ReadFull(body, head)
	if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
		return nil, err
	}
	return head[:n], nil
}

// sniffContentType prefers the magic bytes, then the file extension, and
// falls back to a binary/text split.
func sniffContentType(filename string, head []byte) string {
	detected := mimetype.Detect(head).String()
	generic := strings.HasPrefix(detected, "text/plain") || detected == "application/octet-stream"
	if !generic {
		return detected
	}
	if byExt := mime.TypeByExtension(path.Ext(filename)); byExt != "" {
		return byExt
	}
	if highlight.HasBinaryContent(head) {
		return "application/octet-stream"
	}
	return "text/plain; charset=utf-8"
}

// parseRange reads one `bytes=a-b` or `bytes=-n` range. partial is false
// when the header is absent or unusable.
func parseRange(header string, total int64) (start, length int64, partial bool) {
	spec, ok := strings.CutPrefix(header, "bytes=")
	if !ok || total == 0 {
		return 0, 0, false
	}
	from, to, ok := strings.Cut(spec, "-")
	if !ok {
		return 0, 0, false
	}
	if from == "" {
		n, err := strconv.ParseInt(to, 10, 64)
		if err != nil || n <= 0 {
			return 0, 0, false
		}
		n = min(n, total)
		return total - n, n, true
	}
	start, err := strconv.ParseInt(from, 10, 64)
	if err != nil || start < 0 || start >= total {
		return 0, 0, false
	}
	end := total - 1
	if to != "" {
		n, err := strconv.ParseInt(to, 10, 64)
		if err != nil {
			return 0, 0, false
		}
		end = min(n, total-1)
	}
	if end < start {
		return 0, 0, false
	}
	return start, end - start + 1, true
}

func (s *Server) editFilePage(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.adminRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	filePath := refParam(r, "*")
	branches, _ := s.Git.Branches(r.Context(), repo.Name)
	if !slices.Contains(branches, ref) {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	base, err := s.Git.ResolveRef(r.Context(), repo.Name, ref)
	if err != nil {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	content, err := s.Git.Show(r.Context(), repo.Name, base, filePath)
	if err != nil || len(content) == 0 {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	if highlight.HasBinaryContent(content) {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	views.Render(w, http.StatusOK, views.FileEdit(s.Cfg, User(r), repo, ref, filePath, views.FileForm{
		Content: string(content), Base: base, Error: r.URL.Query().Get("error"),
	}))
}

func (s *Server) editFile(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.adminRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	filePath := refParam(r, "*")
	branches, _ := s.Git.Branches(r.Context(), repo.Name)
	if !slices.Contains(branches, ref) {
		http.Error(w, "Not found", http.StatusNotFound)
		return
	}
	back := "/" + repo.Name + "/edit/" + views.EscapePath(ref) + "/" + views.EscapePath(filePath)

	newPath := strings.TrimSpace(r.FormValue("new_path"))
	targetPath := filePath
	if newPath != "" && newPath != filePath {
		if len(newPath) > maxFilePathBytes || !gitcmd.ValidPath(newPath) {
			s.backTo(w, r, back, "error", "Invalid file path.")
			return
		}
		targetPath = newPath
	}

	message := strings.TrimSpace(r.FormValue("message"))
	if message == "" {
		if targetPath != filePath {
			message = "Rename " + path.Base(filePath) + " to " + path.Base(targetPath)
		} else {
			message = "Edited " + path.Base(filePath)
		}
	}
	content := strings.ReplaceAll(r.FormValue("content"), "\r\n", "\n")

	base := r.FormValue("base")
	commit, err := s.Git.EditFile(r.Context(), repo.Name, ref, base, filePath, targetPath,
		[]byte(content), message, s.committer())
	if err != nil {
		form := views.FileForm{Path: targetPath, Content: content, Message: message, Base: base}
		var stale *gitcmd.StaleError
		switch {
		case errors.As(err, &stale):
			form.Base, form.Stale = stale.Tip, true
			form.Error = "This file changed on " + ref + " since you opened it. " +
				"Saving again overwrites that change."
		case errors.Is(err, gitcmd.ErrExists):
			form.Error = "A file already exists at " + targetPath + "."
		default:
			http.Error(w, "Failed to save file", gitStatusCode(err))
			return
		}
		views.Render(w, http.StatusConflict, views.FileEdit(s.Cfg, User(r), repo, ref, filePath, form))
		return
	}
	redirectTo(w, r, "/"+repo.Name+"/commit/"+commit)
}

func (s *Server) newFilePage(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.adminRepo(w, r)
	if !ok {
		return
	}
	q := r.URL.Query()
	views.Render(w, http.StatusOK, views.NewFileForm(s.Cfg, User(r), repo,
		refParam(r, "ref"), q.Get("dir"), views.FileForm{Error: q.Get("error")}))
}

func (s *Server) createFile(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.adminRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	back := "/" + repo.Name + "/new-file/" + views.EscapePath(ref)

	filePath := strings.TrimSpace(r.FormValue("path"))
	if len(filePath) > maxFilePathBytes || !gitcmd.ValidPath(filePath) {
		s.backTo(w, r, back, "error", "Invalid file path.")
		return
	}
	userMessage := strings.TrimSpace(r.FormValue("message"))
	message := userMessage
	if message == "" {
		message = "Add " + filePath
	}

	branches, _ := s.Git.Branches(r.Context(), repo.Name)
	if len(branches) > 0 && !slices.Contains(branches, ref) {
		s.backTo(w, r, back, "error", "Can only create files on a branch.")
		return
	}
	content := r.FormValue("content")
	commit, err := s.Git.EditFile(r.Context(), repo.Name, ref, "", "", filePath,
		[]byte(content), message, s.committer())
	if errors.Is(err, gitcmd.ErrExists) {
		views.Render(w, http.StatusConflict, views.NewFileForm(s.Cfg, User(r), repo, ref, "", views.FileForm{
			Path: filePath, Content: content, Message: userMessage,
			Error: "A file already exists at " + filePath + ".",
		}))
		return
	}
	if err != nil {
		s.backTo(w, r, back, "error", writeFailMessage(err, "Failed to create file."))
		return
	}
	redirectTo(w, r, "/"+repo.Name+"/commit/"+commit)
}

func (s *Server) deleteFile(w http.ResponseWriter, r *http.Request) {
	repo, ok := s.adminRepo(w, r)
	if !ok {
		return
	}
	ref := refParam(r, "ref")
	filePath := refParam(r, "*")
	message := strings.TrimSpace(r.FormValue("message"))
	if message == "" {
		message = "Delete " + filePath
	}
	commit, err := s.Git.DeleteFile(r.Context(), repo.Name, ref, r.FormValue("base"), filePath,
		message, s.committer())
	if errors.Is(err, gitcmd.ErrNotFound) {
		http.Error(w, "No such file on this branch", http.StatusNotFound)
		return
	}
	var stale *gitcmd.StaleError
	if errors.As(err, &stale) {
		s.renderBlob(w, r, repo, http.StatusConflict, "This file changed on "+ref+
			" since you opened it. The current version is shown below. Delete again to remove it.")
		return
	}
	if err != nil {
		s.backTo(w, r, "/"+repo.Name+"/blob/"+views.EscapePath(ref)+"/"+views.EscapePath(filePath), "error",
			writeFailMessage(err, "Failed to delete file."))
		return
	}
	redirectTo(w, r, "/"+repo.Name+"/commit/"+commit)
}

// writeFailMessage names the concurrent-update case, which the user can fix
// by reloading. Everything else keeps the generic message.
func writeFailMessage(err error, generic string) string {
	if errors.Is(err, gitcmd.ErrRefChanged) {
		return "The branch moved while saving. Please reload and try again."
	}
	return generic
}

// committer is the identity used for commits made through the web UI.
func (s *Server) committer() gitcmd.Ident {
	return gitcmd.Ident{Name: s.Cfg.CommitterName, Email: s.Cfg.CommitterEmail}
}